Publications

MOLECULAR STRUCTURE INVESTIGATIONS BY ELECTRON DIFFRACTION

No abstract is provided for this article.

3R-NbS₂ as a highly stable anode for sodium-ion batteries

3R-NbS 2 obtained from solid-state synthetic route was employed as an SIB anode material and exhibited a remarkable cycling stability for 2500 cycles at 0.5 A g −1 .

Organically Templated Mixed‐Valent Iron Sulfates Possessing Kagome and Other Types of Layered Networks.

For Abstract see ChemInform Abstract in Full Text.

Mesoscale organization of metal nanocrystals

Nanocrystals of metals covered by alkanethiols organize themselves in two-dimensional arrays. We discuss such arrays of metal nanocrystals at length, with focus on the dependence of the structure and the stability of the arrays on the particle diameter and the distance between the particles. Three-dimensional superstructures of metal nanocrystals obtained by the use of alkanedithiols are examined. These ordered two- and three-dimensional structures of thiolized metal nanocrystals are good examples of mesoscale self-assembly. The association of metal nanocrystals to give rise to giant clusters with magic nuclearity provides an even more graphic demonstration of mesoscale self-assembly.

Mechanical properties of nanodiamond-reinforced polymer-matrix composites

Poly(vinyl alcohol)-matrix reinforced with nanodiamond (ND) particles, with ND content up to 0.6 wt%, were synthesized. Characterization of the composites by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) reveal uniform distribution of the ND particles with no agglomeration in the matrix. Differential scanning calorimetry reveals that the crystallinity of the polymer increases with increasing ND content, indicating a strong interaction between ND and PVA. Nano-indentation technique was employed to assess the mechanical properties of composites. Results show that even small additions of ND lead to significant enhancement in the hardness and elastic modulus of PVA. Possible micromechanisms responsible for the enhancement of the mechanical properties are discussed.

Barkhausen jumps and related magnetic properties of iron nanowires encapsulated in aligned carbon nanotube bundles

Iron nanowires encapsulated in aligned carbon nanotube bundles show interesting magnetic properties. Besides the increased coercivity, Barkhausen jumps with 5 emu/g steps in magnetization are observed due to magnetization reversal or depinning of domains.

HIGH-T_csuperconductivity in perovskite oxides of the Y─Ba─Cu─O system

Several biphasic compositions of the type Y3−xBa3+xCu6O14 show an onset of superconductivity in the 90-115K range, attaining zero resistance in the 70-85K range. The phase responsible for superconductivity in these compositions is a perovskite oxide of composition YBa2Cu3 O7. This oxide annealed in oxygen shows the onset of superconductivity at 120K and zero resistance at 87K. YBa2,Cu3O7 shows the highest Meissner effect of all oxide superconductors. The superconducting behaviour of the two perovskite oxides, Y0.95Ba1.95,Cu3O7 and Y1.05Ba1.95Cu3O7 show interesting features; a marked decrease in resistivity is observed from room temperature itself in the former oxide with zero resistance at 89K. Electron microscopy and infrared spectra of these oxides are briefly discussed.

Reentrant transition from an incipient charge-ordered state to a ferromagnetic metallic state in a rare-earth manganate

A reentrant transition from an incipient charge-ordered (CO) state to a charge-delocalized ferromagnetic (CDFM) state has been established in the manganate ${\mathrm{Nd}}_{0.25}{\mathrm{La}}_{0.25}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3},$ in which the average $A$-site ionic radius is 1.19 \AA{}. The reentrant CDFM phase is associated with a first-order phase transition that reduces the orthorhombic distortion of the lattice, in contrast to the CO transition in other manganates where the orthorhombically distorted CO state is stabilized at low temperatures. At the CO-CDFM transition, there is a collapse of the charge-ordering gap as measured by vacuum tunneling spectroscopy.

Optical limiting in single-walled carbon nanotube suspensions

Optical limiting behaviour of suspensions of single-walled carbon nanotubes in water, ethanol and ethylene glycol is reported. Experiments with 532 nm, 15 ns duration laser pulses show that optical limiting occurs mainly due to nonlinear scattering. The observed host liquid dependence of the optical limiting effect in different suspensions suggests that the scattering originates from microbubbles formed due to absorption-induced heating.

Effect of Cation Size and Disorder on the Structure and Properties of the Rare Earth Cobaltates, Ln_0.5A_0.5CoO₃ (Ln = Rare Earth, A = Sr, Ba)

The structure of Ln0.5Sr0.5CoO3 is rhombohedral (R3̄c) when Ln = La, Pr, or Nd, but orthorhombic (Pnma) when Ln = Gd. The Ln0.5Ba0.5CoO3 compounds, except for Ln = La, are orthorhombic (Pmmm). The ferromagnetic Curie temperature, TC, of Ln0.5A0.5CoO3 increases with the average size of the A-site cation up to an 〈rA〉 of 1.40 Å, and decreases thereafter due to size mismatch. Disorder due to cation-size mismatch has been investigated by studying the properties of two series of cobaltates with fixed 〈rA〉 and differing size variance, σ2. It is found that TC decreases linearly with σ2, according to the relation, TC = T°C − pσ2. When σ2 is large (>0.012 Å2), the material becomes insulating, providing evidence for a metal−insulator transition caused by cation-size disorder. Thus, Gd0.5Ba0.5CoO3 with a large σ2 is a charge-ordered insulator below 340 K. The study demonstrates that the average A-cation radius, as well as the cation-size disorder, affects the magnetic and transport properties of the rare earth cobaltates significantly.

Photophysical properties of the fullerenes, C60 and C70

Photophysical properties of the singlet and triplet states of the fullerenes, C60 and C70, have been investigated in toluene, benzene, hexane and ethanol solutions by pico- and nano-second laser flash photolysis techniques. Lifetimes, extinction coefficients, quantum efficiencies of the formation of the excited states and such properties have been determined. True triplet—triplet absorption spectra of C60 and C70 are reported. C60, unlike C70, is found to undergo photoionization in ethanol solution giving solvated electrons.

Relation between Tc and hole concentration in superconducting cuprates

The superconducting transition temperature, T c, of several series of cuprates shows a nonlinear dependence on the hole concentration, n h, determined by chemical titrations. The t c becomes maximum when n h is in the 0.12-0.15 range in cuprates containing a single Cu-O layer and around 0.2 in cuprates containing two Cu-O layers.

Open-Framework Cadmium Succinates of Different Dimensionalities

Open-framework cadmium succinates, [CN(3)H(6)](2)[Cd(2)(C(4)H(4)O(4))(Cl)(2)], I; [CN(3)H(6)](2)[Cd(C(4)H(4)O(4))(2)], II; Cd(2)(C(4)H(4)O(4))(2)(C(4)N(2)H(8))(H(2)O)(3), III; [C(4)N(2)H(12)][Cd(2)(C(4)H(4)O(4))(3)].4H(2)O, IV; Cd(C(4)H(4)O(4))(H(2)O)(2), V; and Cd(3)(C(4)H(4)O(4))(2)(OH)(2)], VI, of different dimensionalities have been synthesized by hydrothermal procedure by employing two different strategies, one involving the reaction of Cd salts with organic-amine succinates and the other involving the hydrothermal reaction of Cd salts with a mixture of succinic acid and the organic amine. While the latter procedure yields structures without any amine in them, the former gives rise to amine templated cadmium succinates with open architectures. By employing guanidinium succinate we have obtained I and II, and with piperazinium succinate we obtained III and IV. Of these I has a one-dimensional chain structure, IV has a layered structure, and II and III have three-dimensional architectures. The two cadmium succinates without incorporation of amine, V and VI, possess layered and three-dimensional structures, respectively. The three-dimensional structures II and III exhibit interpenetration similar to that in diamondoid and alpha-polonium type structures, respectively.

Structure–Property Relationships in Superconducting Cuprates

Some interesting phase transitions in solids

No abstract is provided for this article.

Calorimetric, infrared and ESR studies of the plastically crystalline state of organic compounds

Enthalpy changes of the crystal-plastic and plastic-liquid transitions are related to the temperature range of stability of the plastic phase. Thermodynamics of the plastic state of binary mixtures have been examined. Infrared correlation times, τc, and activation energies have been measured for a few molecules in the plastic state. Molecular tumbling times, τt, have also been measured employing ESR spectra of a spin-probe. Plots of log τc(τt) versus 1/T are continuous through the plastic-liquid transition. Activation energies for molecular motion seem to vary in the same direction as the ΔH of the plastic-crystal transition. Infrared correlation times of solute molecules in binary solutions in the plastic and the liquid states show interesting variations with solute concentration.

GaS and GaSe Ultrathin Layer Transistors

Room-temperature, bottom-gate, field-effect transistor characteristics of 2D ultrathin layer GaS and GaSe prepared from the bulk crystals using a micromechanical cleavage technique are reported. The transistors based on active GaS and GaSe ultrathin layers demonstrate typical n-and p-type conductance transistor operation along with a good ON/OFF ratio and electron differential mobility. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Computer simulation of quenched liquids: the glassy state of water

Monte Carlo simulation of liquid water quenched to low temperatures has been carried out in the NPT ensemble. The quenched system shows a glass-like transition and a distribution of hydrogen-bonded species different from the liquid.